This disclosure generally relates to methods and systems for measuring a quantity of liquid fuel in a fuel tank, such as a storage tank or other container. More particularly, this disclosure relates to methods and systems for measuring the quantity of liquid fuel in a fuel tank in a manner that does not require the presence of electrical components in the fuel tank.
A need to continuously measure the quantity of liquid fuel in a fuel tank exists in many commercial and military applications. For example, liquid-level sensors are commonly used in the fuel tanks of aircraft, automobiles, and trucks. Liquid-level sensors are also used to monitor liquid levels within storage tanks used for fuel dispensing.
Many transducers for measuring liquid level employ electricity. The electrical output of such transducers changes in response to a change in the liquid level being measured, and is typically in the form of a change in resistance, capacitance, current flow, magnetic field, frequency, and so on. These types of transducers may include variable capacitors or resistors, optical components, Hall Effect sensors, strain gauges, ultrasonic devices, and so on.
Currently most fuel sensors on aircraft use electricity. For example, existing electrical capacitance sensors require electrical wiring inside the tank, which in turn requires complex installations and protection measures to preclude a safety issue under certain electrical fault conditions. This electrical wiring requires careful shielding, bonding, and grounding to minimize stray capacitance and further requires periodic maintenance to ensure electrical contact integrity.
In the cases of commercial and military aviation, it is important for the flight crew to know there is adequate fuel upload for a mission prior to each flight. It is equally important for the crew to know during the flight that there is adequate fuel remaining in the tanks to complete each flight safely. A simple and accurate fuel quantity gauging system is needed. For a typical long-range transport aircraft, it takes a quarter to a half pound of fuel to transport a pound of weight. Extra fuel is dead weight and it takes fuel to transport that extra weight.
It would be advantageous if the amount of liquid fuel in a fuel tank could be measured without introducing electrical current into the fuel tank and without using optical techniques.